Mackinac Bridge Indefinite Delivery Services—St. Ignace, MI

The Mackinac Bridge (pronounced ma·kuh·naaw) is a 5-mile-long structure that connects the upper and lower peninsulas of Michigan over the Straits of Mackinac. It was originally designed by Steinman and completed in 1957. Steinman was subsequently acquired by Parsons, in 1989, and became a our New York office center of excellence for our Bridge Technical Organization (BTO).

Our Scope Of Services

Bridge Inspection & Analysis

We have performed more than 75 Annual, Fracture Critical and special main cable interior Inspections of the structure since its construction in 1957. In addition to this, we have performed numerous state of good repair design services of the structure as well as numerous types of analysis including load ratings, wind performance analysis and wind tunnel testing and other types of permit loading analysis as required.

Since 1957, we have supported the Mackinac Bridge Authority with ongoing inspection, analysis, and rehabilitation of the Mackinac Bridge, one of the most significant long-span suspension bridges in North America. Our team has conducted 19 in-depth main cable inspections, unwrapping more than 20, 38-foot panels to wedge open and assess interior wires, plus inspection of the suspender cables, sockets, cable bands, splay strands, and anchorages. Parsons also designed and fabricated specialized equipment—including a cable compactor and wrapping machine—to restore each panel after inspection

Component Analysis And Design

In addition to the services described above, we have performed numerous assignments involving element and global analysis (2D and 3D structure modeling) of the Mackinac Bridge, as well as design of component retrofitting, element design, detailing, and oversight of shop fabrication and field work. These have included steel and concrete elements, steel grid deck elements, cable elements, and movable components such as bearings, hanger links, and the new access travelers for the truss and suspended spans. Since 1921 we have experience in structural analysis and design of major suspension bridges, benefiting the MBA in lessons-learned.

Gusset Plate Design And Field Inspection

We provided engineering design, structural evaluation, and field inspection of the gusset plates for 30 deck truss spans (total over 9,300 feet). The work included field inspection, measurement, and detailed analysis of gussets in accordance with latest FHWA and MDOT requirements followed by preparation of a detailed report documenting the findings of both the field inspection and structural analysis.

The Mackinac Deck Study

At a public meeting on July 8, 2021, we presented a report to the Mackinac Bridge Authority that outlined a 17-year capital program for the bridge’s full deck replacement, which is the largest project in the authority’s history.

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Suspended Main Span Expansion Joint Replacement

We also provided engineering design as well as a quality assurance program, construction support services engineering, and material procurement for replacement of the main expansion joints at both towers of the 3,800-foot suspended main span. Each of the joints measured 38 feet by 60 feet and were designed to accommodate movement about all three axis. Parsons provided all the engineering design details, the staging scheme for removal and reinstallation of this joints, as well as the design and construction specifications and shop fabrication support.

Tower Hanger Link Replacement

We also prepared engineering design, provided construction support services engineering, and material procurement for the replacement of a main tower hanger link at the south tower of the bridge. Parsons also developed the engineering design, analysis, and construction support services engineering for the temporary supports that were used to support 350 tons of main bridge structure.

Celebrating Our Engineering Partnership With The Mackinac Bridge Authority